Re: [PATCH 06/14] block/nbd: further segregation of connect-thread

[Roman Kagan <rvkagan@yandex-team.ru>]

On Wed, Apr 07, 2021 at 01:46:29PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Add personal state NBDConnectThread for connect-thread and
> nbd_connect_thread_start() function. Next step would be moving
> connect-thread to a separate file.
> 
> Note that we stop publishing thr->sioc during
> qio_channel_socket_connect_sync(). Which probably means that we can't
> early-cancel qio_channel_socket_connect_sync() call in
> nbd_free_connect_thread(). Still, when thread is detached it doesn't
> make big sense, and we have no guarantee anyway.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/nbd.c | 57 ++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 39 insertions(+), 18 deletions(-)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index e16c6d636a..23eb8adab1 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -85,8 +85,6 @@ typedef enum NBDConnectThreadState {
>  } NBDConnectThreadState;
>  
>  typedef struct NBDConnectCB {
> -    /* Initialization constants */
> -    SocketAddress *saddr; /* address to connect to */
>      /*
>       * Bottom half to schedule on completion. Scheduled only if bh_ctx is not
>       * NULL
> @@ -103,6 +101,15 @@ typedef struct NBDConnectCB {
>      AioContext *bh_ctx; /* where to schedule bh (NULL means don't schedule) */
>  } NBDConnectCB;
>  
> +typedef void (*NBDConnectThreadCallback)(QIOChannelSocket *sioc, int ret,
> +                                         void *opaque);
> +
> +typedef struct NBDConnectThread {
> +    SocketAddress *saddr; /* address to connect to */
> +    NBDConnectThreadCallback cb;
> +    void *cb_opaque;
> +} NBDConnectThread;
> +
>  typedef struct BDRVNBDState {
>      QIOChannelSocket *sioc; /* The master data channel */
>      QIOChannel *ioc; /* The current I/O channel which may differ (eg TLS) */
> @@ -367,7 +374,6 @@ static void nbd_init_connect_thread(BDRVNBDState *s)
>      s->connect_thread = g_new(NBDConnectCB, 1);
>  
>      *s->connect_thread = (NBDConnectCB) {
> -        .saddr = QAPI_CLONE(SocketAddress, s->saddr),
>          .state = CONNECT_THREAD_NONE,
>          .bh_func = connect_bh,
>          .bh_opaque = s,
> @@ -378,20 +384,18 @@ static void nbd_init_connect_thread(BDRVNBDState *s)
>  
>  static void nbd_free_connect_thread(NBDConnectCB *thr)
>  {
> -    if (thr->sioc) {
> -        qio_channel_close(QIO_CHANNEL(thr->sioc), NULL);
> -    }

Doesn't this result in an open channel leak?  (The original code here
seems to be missing an unref, too.)

> -    qapi_free_SocketAddress(thr->saddr);
>      g_free(thr);
>  }
>  
> -static void connect_thread_cb(int ret, void *opaque)
> +static void connect_thread_cb(QIOChannelSocket *sioc, int ret, void *opaque)
>  {
>      NBDConnectCB *thr = opaque;
>      bool do_free = false;
>  
>      qemu_mutex_lock(&thr->mutex);
>  
> +    thr->sioc = sioc;
> +
>      switch (thr->state) {
>      case CONNECT_THREAD_RUNNING:
>          thr->state = ret < 0 ? CONNECT_THREAD_FAIL : CONNECT_THREAD_SUCCESS;
> @@ -418,27 +422,45 @@ static void connect_thread_cb(int ret, void *opaque)
>  
>  static void *connect_thread_func(void *opaque)
>  {
> -    NBDConnectCB *thr = opaque;
> +    NBDConnectThread *thr = opaque;
>      int ret;
> +    QIOChannelSocket *sioc = qio_channel_socket_new();
>  
> -    thr->sioc = qio_channel_socket_new();
> -
> -    ret = qio_channel_socket_connect_sync(thr->sioc, thr->saddr, NULL);
> +    ret = qio_channel_socket_connect_sync(sioc, thr->saddr, NULL);
>      if (ret < 0) {
> -        object_unref(OBJECT(thr->sioc));
> -        thr->sioc = NULL;
> +        object_unref(OBJECT(sioc));
> +        sioc = NULL;
>      }
>  
> -    connect_thread_cb(ret, thr);
> +    thr->cb(sioc, ret, thr->cb_opaque);
> +
> +    qapi_free_SocketAddress(thr->saddr);
> +    g_free(thr);
>  
>      return NULL;
>  }
>  
> +static void nbd_connect_thread_start(const SocketAddress *saddr,
> +                                     NBDConnectThreadCallback cb,
> +                                     void *cb_opaque)
> +{
> +    QemuThread thread;
> +    NBDConnectThread *thr = g_new(NBDConnectThread, 1);
> +
> +    *thr = (NBDConnectThread) {
> +        .saddr = QAPI_CLONE(SocketAddress, saddr),
> +        .cb = cb,
> +        .cb_opaque = cb_opaque,
> +    };
> +
> +    qemu_thread_create(&thread, "nbd-connect",
> +                       connect_thread_func, thr, QEMU_THREAD_DETACHED);
> +}
> +
>  static int coroutine_fn
>  nbd_co_establish_connection(BlockDriverState *bs)
>  {
>      int ret;
> -    QemuThread thread;
>      BDRVNBDState *s = bs->opaque;
>      NBDConnectCB *thr = s->connect_thread;
>  
> @@ -448,8 +470,7 @@ nbd_co_establish_connection(BlockDriverState *bs)
>      case CONNECT_THREAD_FAIL:
>      case CONNECT_THREAD_NONE:
>          thr->state = CONNECT_THREAD_RUNNING;
> -        qemu_thread_create(&thread, "nbd-connect",
> -                           connect_thread_func, thr, QEMU_THREAD_DETACHED);
> +        nbd_connect_thread_start(s->saddr, connect_thread_cb, thr);
>          break;
>      case CONNECT_THREAD_SUCCESS:
>          /* Previous attempt finally succeeded in background */
> -- 
> 2.29.2
>